I don't lend that Guardian article much creedence- it uses all the standard journalism/public health tricks to make its argument.
"Potassium bromate, a potent oxidizer that helps bread rise, has been linked to kidney and thyroid cancers in rodents."
if something is "linked to ... cancers in rodents", that tells us basically nothing about its safety in the industrial process and consumption by humans.
> the additives used in the making of American bread
...but far from all US bread. You tend to find the more questionable additives in the cheapest store-bought breads. But it's also not hard to find higher-quality bread that omits them.
Now a comparison of US vs. EU cases of early onset colorectal cancer would be required.